1. Field of the Invention
The present invention is directed to a touch sensor for an electronic display system. More specifically, the present invention relates to feedlines of a self-capacitive touch sensor provided directly on an electronic display panel and a method of fabricating the same.
2. Description of the Related Art
An electronic display is a device, panel, or screen that visually presents images, text, or video that is transmitted electronically. Examples of electronic displays are used as components in televisions, computer monitors, digital signage, smart phones, and tablet computers. Display devices can either emit light, i.e., emissive type, or modulate light, i.e., non-emissive type.
An organic light emitting-diode (OLED) display device is an emissive type electronic display that includes an organic light emitting display panel and driver electronics to control the organic light emitting display panel. The organic light emitting display panel includes a matrix of pixels with each pixel including an organic light emitting-diode and a driving thin-film transistor (TFT). OLED displays are multi-color with a wide viewing angle, high contrast, and fast response speed.
An OLED display panel includes a pixel layer having colored sub-pixels, typically a combination of red, green, and blue (R, G, B). The pixel layer is typically constructed with two electrodes and an organic light-emitting layer between the two electrodes. The two electrodes include an anode electrode and a cathode electrode, which are applied with different voltages. The pixel layer is usually protected by an encapsulation or a sealing layer that may include multiple thin layers or a sealing substrate.
A liquid crystal display (LCD) is a non-emission type display that includes a liquid crystal panel and driver electronics to control the liquid crystal panel. LCD panels include a series of cells that can each be driven independently to modulate input light. An active-matrix liquid-crystal display (AMLCD) includes a matrix of cells or sub-pixels with each sub-pixel including a switching TFT. The TFTs store the electrical state of each sub-pixel on the display while all the other sub-pixels are being updated. The sub-pixels typically include a corresponding red, green, or blue color filter driven in combination to form a color gamut.
A typical LCD includes an array substrate including the TFTs and connecting signal lines, an opposing substrate including the color filter, and a liquid crystal layer in between the two substrates. The driving electronics are used to create a voltage potential between a pixel electrode and a common electrode at each pixel to modulate adjacent liquid crystals in the liquid crystal layer.
The OLED displays and LCDs are increasingly popular, but other pixelated emissive and non-emissive type electronic display technologies are also well known.
Touch screens are widely used with electronic displays, especially for smart phones and mobile electronic devices. A touch sensor or screen is an input device that can be joined with an electronic display device to facilitate user interaction and control. Such devices typically include a touch screen mounted on a surface of an electronic display that displays interactive information.
Touch screens detect the location of an external touch or gesture of a finger, stylus, or similar object that occurs at or near the surface of the touch screen. Such touch screens include a matrix of transparent conductive elements or electrodes that form a touch sensor that overlay the display device and separate control electronics to determine the location of the touch object near or in contact with the touch sensor. Touch screens are typically transparent so the user can view displayed information on the display device through the touch-screen. By physically touching, or nearly touching, the touch sensor in a location associated with displayed information, a user can select an operation associated with the displayed information. The touch sensor detects the touch and then electronically interacts with the control electronics, or controller, to determine and output the touch location. The output signal of the touch location is input to a processor that associates the touch location or gesture with the displayed information to execute a programmed task associated with the displayed information as a graphic user interface.
Touch screens can use a variety of technologies, including resistive, inductive, capacitive, acoustic, piezoelectric, and optical technologies, to locate a touch or gesture on a sensor.
Capacitive touch-screens are of at least two different types: self-capacitive and mutual-capacitive. Self-capacitive touch-screens use an array of transparent electrodes on the sensor in combination with the touching object to form a temporary capacitor, a capacitance of which is detected. Mutual-capacitive touch-screens use an array of transparent electrode pairs that form capacitors, a capacitance of which is affected by the touching object. In both types, each capacitor in the array is sensed to detect a touch, and the physical location of the touch-detecting electrode in the touch-screen corresponds to the location of the touch.
As mentioned, touch sensors are typically transparent or formed to be invisible to the user and minimize optical distractions and artifacts. While interacting with the display panel, the touch sensor should minimize ambient reflection, maximize display transmission, not significantly reduce the range of possible viewing angles, and not cause any Moiré patterns or other optical interference effects. Electrically, the touch sensor should be highly conductive and uniform to maximize sensitivity and minimize voltage potential gradients. Touch sensors are either transparent conductive materials or conductive elements that are spaced apart and are too small to be seen by the user.
A typical transparent touch sensor includes a patterned coating of a conventional transparent conducting material (TCM) such as a transparent conducting oxide (TCO) or indium tin oxide (ITO). Disadvantages of such designs include limited transparency and conductivity and increased sensitivity to mechanical or environmental stress. Thicker layers of conventional TCM increase conductivity and resistance to stress but reduce the transparency of the electrodes.
For increased conductivity and to overcome issues of touch sensors made from conventional TCM, touch screen sensors can be made from grid patterns of fine metal wires, meshes, or conductive traces. These micro-wires are opaque, but are meant to be fine enough and spaced apart so that they are normally not detectable by the user. Although more uniformly conductive than conventional TCM designs, patterns of micro-wire electrodes can visibly interact with pixels in a display and cause Moiré patterns and other optical interference artifacts.
In order to reduce the device thickness as much as possible, the touch sensor can be formed directly on the display, and the display and touch sensor can be manufactured in the same process. This can result in the reduction of production costs compared with production of the display and touch sensor as separate components and subsequently combining them together. However, because a manufacturing defect in the touch sensor results in the wasted production of the display, features that increase the manufacturing yield of the touch sensor are desired.